The Session Initiation Protocol (SIP) is a protocol for creating, modifying, and terminating computer network-based communication sessions, such as for an Internet-based telephone call between two or more participants. Since its introduction various enhancements to SIP have been proposed, including the SIP Instant Messaging and Presence Leveraging Extensions (SIMPLE) framework in which one or more network entities, such as computer users, create subscriptions on a server, known as a “presence” server, to receive presence information regarding another network entity, referred to as a “presentity.” When a change in the presentity's presence information is detected, such as when the presentity “publishes” such a change to the presence server, SIP is used to send a notification to the subscribers including the presentity's current presence information.
Further enhancements to SIP/SIMPLE include enabling presentities to limit what presence information subscribers may receive in a notification, as well as enabling subscribers to limit what available presence information they wish to receive in a notification. For example, presentity Joe's presence information includes elements ABCDE, while Joe limits subscriber Bob to receive only elements BCDE. If a change occurs to any of elements ABCDE, the presence server managing Bob's subscription will send Joe a notification including elements BCDE. However, if the change is to element A, and Bob previously received a notification including elements BCDE, Bob will receive no new information in the notification, as Bob previously received elements BCDE and does not in any case receive element A. Similarly, if Bob is only interested in elements DE, and sets a notification filter accordingly, if the change is to any of elements ABC, and Bob previously received a notification including elements DE, Bob will receive no new information in the notification, as Bob only ever receives elements DE. In both these examples, the changes to Joe's presence information caused redundant notifications to be sent to Bob, needlessly consuming processing and bandwidth resources.
Systems and/or methods for eliminating redundant notifications to SIP/SIMPLE subscribers would therefore be advantageous.